Method for printing a substrate using an anilox roll, an anilox roll for a printing method and a printing apparatus

ABSTRACT

The invention relates to an anilox roll for a printing apparatus. The anilox roll comprises a cylinder having a surface. The surface comprises a fluid distribution structure for receiving, distributing and transferring a fluid such as an ink. The fluid distribution structure comprises a channel formed in the surface having channel walls. This channel is arranged for distributing the fluid over the fluid distribution structure. The channel comprises channel parts, wherein the courses of connected channel parts are at an angle with respect to each other for preventing a linear distribution of the fluids to be received in a course direction of the channel, allowing a meandering distribution of the fluid to be received in the channel. Side walls of the channel are arranged for allowing a meandering flow of the fluid throughout the fluid distribution surface.

CLAIM OF PRIORITY

The present application is a division of U.S. patent application Ser.No. 12/529,750, entitled “METHOD FOR PRINTING A SUBSTRATE USING ANANILOX ROLL, AN ANILOX ROLL FOR A PRINTING METHOD AND A PRINTINGAPPARATUS” by Hendriks, filed Sep. 3, 2009, which is a 371 ofInternational Patent Application No. PCT/NL08/50841, entitled “A METHODFOR PRINTING A SUBSTRATE USING AN ANILOX ROLL, AN ANILOX ROLL FOR APRINTING METHOD AND A PRINTING APPARATUS” by Hendriks, filed Dec. 22,2008, which claims priority to NL200113 filed Dec. 21, 2007 and NL200115filed Dec. 21, 2007, which applications are herein incorporated byreference.

FIELD OF INVENTION

The invention relates to an anilox roll. The invention also relates toprinting of substrates wherein use is made of an anilox roll. Theinvention further relates to a printing apparatus, comprising an aniloxroll. The invention also concerns using and forming an anilox roll.

BACKGROUND

Anilox rolls have been used in flexographic methods in the printingindustry. This printing method was used generally for printing differentsubstrates, such as papers, labels, tape, (plastic) bags and boxes.Anilox rolls can be used in printing methods other than flexographicmethods. Also offset printing and intaglio. An anilox roll is used inthese other methods for transferring ink in precise and constantamounts.

SUMMARY

An anilox roll comprises a generally hard cylinder, having a core ofsteel or aluminium. On top of the core a thin layer of ceramics isprovided. In the thin layer usually small ink cells, hereafter cells,are engraved. In a known embodiment cells are formed having a hexagonalor honeycomb pattern on the surface of the anilox roll. The cells have avolume for receiving ink as a function of the size of the cell and depthof the cell. The size of the cells on the surface of the anilox rollwill determine the density of cells. The density of cells is expressedin lines per linear centimeters. The volume of the cell will determinethe operational mode of the anilox roll. Patterns and cells on thesurface of the anilox roll can be formed using a laser by performing alaser engraving method. The method can comprise a continuous orpulsating laser. The laser is directed onto the surface of the aniloxroll forming a laser spot and the laser spot will engrave a pattern ontothe surface. The intensity of the laser is sufficient for locallyvaporising the material of the outer layer of the anilox roll, forexample chromium oxide. This will form a cell. A cell comprises a localrecess in the surface of the roll surrounded by cell walls. A singlecell wall can be a wall for two adjacent cells, separating the cells.

The anilox roll is mounted by bearings in a printing apparatus such as aflexographic apparatus. The anilox roll comprises longitudinal ends ofthe cylinder that can be mounted onto a frame of the printing apparatus.The anilox roll is releasably mounted in order to allow cleaning orradid changing. The anilox roll can rotate about its longitudinal axisin a circumferential direction.

The rotating anilox roll can be partially emerged in a ink fountain or afountain roll is partially emerged in an ink fountain, said fountainroll being in contact with the anilox roll for transferring the ink ontothe anilox roll and into the cells. In operation the printing apparatuscomprising the anilox roll will operate to transfer ink onto the surfaceof the anilox roll and the surface structure is arranged for retainingthe ink on and in the surface. The ink is viscous. A blade is used toscrape surplus of ink from the anilox roll or the ink roll. Ink willremain in the cells formed on the surface of the anilox roll.

In operation the anilox roll will rotate and the surface of the aniloxroll will contact a rotatable printing cylinder. The printing cylinderwill receive in an operational mode of the anilox roll a part of the inkcollected on/in the surface of the anilox roll. The amount oftransferred ink will depend on the image to be printed. The printingcylinder will transfer the ink in the next step onto the substrate. Aproblem in transferring the ink from the anilox roll onto the printingroll is that ink can remain in this formed cells on the surface of theanilox roll. The viscosity of the ink as well as the speed of theprinting process can result in ink remaining on the anilox roll. Thiswill effect the printing the substrate. Further ink residue will remainin the cells.

After a partial transfer of the ink from the surface of the anilox roll,that part of the surface will rotate further and will once again reachthe ink roll or ink fountain. The cells can function as an air pumpbringing air into the ink resulting in foaming of the ink, and said airin the cells will limit transfer of ink into the cell. The air in thecells should be replaced by ink and a certain amount of time is neededfor making such a replacement, limiting the speed of rotation andfinally the printing speed.

The desired colour intensity of the substrate to be printed willinfluence directly the volume of the cells. If the volume of the cellsis increased, more ink will be printed on the substrate, intensifyingthe resulting colour. Heavy layers of ink are formed on the substrateusing cells having a relatively large volume, transferring relativelylarge droplets of ink, while details in printing are obtained usingcells having a relatively small volume.

The density of cells is expressed in lines per centimeter. Known linescreens for prior art cell-like surface structures are for example100-180 lines per centimeter. The different line screens have specificpurposes. An anilox roll having 100 lines per centimeter is well suitedfor printing heavy layers of ink on a substrate. A relatively largevolume of ink will be transferred in an operational mode of the aniloxroll. Anilox rolls having 180 lines per centimeter will have a highresolution, making them more suitable for printing details on asubstrate. Rolls having a higher line screen will transfer droplets ofink having a relatively smaller volume which will result in transferringless ink in total in this operational mode of the anilox roll. An aniloxroll having a high line screen is less suitable for printing heavylayers of ink.

In prior art printing methods a balance is to be found between highresolution and colour intensity. A higher line screen can be providedwith cells having more depth. This would increase the cell volume.However, in practice using cells of increased depth will result in anincrease of ink residue remaining in the cell. Not all ink from the cellwill be transferred onto the printing roll. Therefore still the printedsubstrate will not show the desired colour intensity.

One of the problems of prior art anilox rolls is the fact that an aniloxroll can only have a single line screen. Known anilox rolls do not allowprinting an image on a substrate wherein the image comprises both heavylayers of ink and details. Replacing an anilox roll is a time consumingand costly process, since printing will be disabled temporarily anddifferent anilox rolls having different line screens are to be provided.

Another problem in relation to known anilox rolls is the necessity ofrepeatedly cleaning the anilox rolls as a result of ink remaining incells of the anilox rolls. This is due to the fact of the cell nature ofthe anilox roll. This will also result in waste of ink. Ink ofsubsequent printing processes will collect in the cells. The propertiesof the anilox roll will deteriorate. The anilox roll will have to becleaned regularly. This is a time consuming and difficult process.

It is therefore a goal of the invention to alleviate or reduce at leastone of the known problems of the anilox rolls. Another goal can be toprovide improved methods for forming an anilox roll.

An improved anilox roll is provided by the invention. The anilox rollcomprises a cylinder having a roll surface. In the surface a fluiddistribution structure is arranged for receiving, distributing andtransferring a fluid such as an ink. The fluid can be a liquid or pastymass. The fluid distribution structure comprises a channel formed in thecylinder for distributing fluid over the fluid distribution structure. Achannel improves fluid transfer properties in respect of cells. Fluid isreceived more easily in a channel, and a channel is cleaned more easily.A channel comprises a recess formed in the surface of the anilox rollthat is surrounded by channel walls. The channel has a course. that isgenerally parallel to the direction of the channel walls at both sidesof the channel part. The channel walls can locally converge of diverge.

In an embodiment the fluid distribution structure is arranged totransfer in a first operational mode for printing heavy layers of ink asuitable, relatively large fluid droplet and in a second operationalmode for printing details a suitable relatively small fluid droplet.This is allowed according to the invention by a suitable combination ofrestrictions provided in the fluid distribution structure, wherein arestriction is formed by a local change of at least one of channel depthand/or channel width and/or channel form and/or channel wall. In one andthe same distribution structure both functionalities, details and heavylayers, are arranged on the same surface depending on the operationalmode.

An operational mode of the anilox roll is a functional behaviour duringtransfer of the fluid for printing substrate. When printing details,relatively small ink amounts are desired and for printing heavy layersof ink relatively large ink amounts are desired. An anilox rollaccording to this embodiment combines the two properties by providingrestrictions formed on the surface of the anilox roll.

In an embodiment the relatively small droplets suitable for printingdetails are provided by open cells formed in the fluid distributionstructure surrounded only partially by channel walls. The open cells areat least partially interconnected, allowing formation of a droplet sizein the first operational mode that is suitable for printing heavy layersof ink by combining the volume of ink from different cells.

A restriction according to an embodiment comprises a change in thecourse of a channel or in particular a channel part. This allows forminga meandering channel. Ink can be distributed over the surface of theanilox roll in the channel. But the distribution is hindered by themeandering of the channel.

The anilox roll comprises in an embodiment for the first operationalmode a fluid distribution structure comprising a meandering channel overthe surface of the roll. The meandering channel forms a restriction. Inthe channel a relative large ink volume is received. The meanderingchannel forms a device for printing a heavy layer of ink. The device forprinting a heavy layer of ink is part of the fluid distributionstructure. The restrictions cooperate to form a structure of relativesmall volumes in the channel, however these volumes can be combined toform a relatively large droplet of ink in dependency of the operationalmode. The operational mode is determined by the transfer of fluid fromthe anilox roll onto the printing roll. The printing roll comprises theimage to be printed. The image can comprise details or a heavy layer ofink or another ink volume image and determines the amount of ink to betransferred.

In an embodiment the anilox roll comprises for the second operationalmode channel parts formed in the, preferably meandering, channel, saidchannel parts having a droplet volume that is suitable for printingdetails. The channel parts form a device for printing details that isformed in the fluid distribution structure. Every channel part isarranged for transferring a fluid droplet of relatively small size toallow printing details. The channel part, on at least two opposite sidessurrounded by channel walls, forms a restriction that allows aparticular operational mode.

In an advantageous embodiment the device for printing a heavy layer ofink and the device for printing details overlap, allowing one and thesame channel part to function according to the operational mode asdetermined by the ink transferring properties of the printing roll.

In an embodiment adjacent channel parts are positioned at an angle withrespect to each other for preventing a linear distribution of fluidreceived in that channel in a course direction of that channel. As thechannel parts are connected and the course of the channel parts arepositioned at an angle, the formed channel will allows a meanderingdistribution of the received fluid in the channel.

In an embodiment the formed connection is relatively large with respectto the droplet size, and allow a droplet to move in between adjacentchannel parts, although the angle and the meandering form of the channelprevent linear distribution of the ink.

In an embodiment of an anilox roll different channel parts can beindicated/recognized by a skilled person. Still a channel can be arelatively continuous, preferably also meandering, combination ofchannel parts that collectively form the fluid structure. Side walls ofthe channel do allow meandering distribution of the fluid received inthe channel. The side walls of the channel are arranged for meandering aflow of ink throughout the fluid distribution structure, but alsorestrict linear flow. The ink can be received into the channels, but canalso be transferred for printing the substrate.

It is noted that U.S. Pat. No. 4,819,558 in the name van C. J. Counarddiscloses an anilox roll. The disclosed anilox roll comprises a cellstructure of diamond shaped cells having a pyramid shaped depth. At thesurface of the anilox roll two cells are connected by a straight channelof limited depth. In U.S. Pat. No. 4,819,558 the channel is not arrangedfor allowing two operational modes to be combined and to overlap in asingle surface, and in particularly U.S. Pat. No. 4,819,558 does notdisclose a channel having channel parts that combine to form a channelwherein the channel course is angled. The disclosed structure will allowonly one operational mode in dependence of the size of the cells. Sidewalls of the channels are not arranged for allowing a meandering flow offluid over de fluid distribution structure. The structure of the surfaceof the anilox roll according the U.S. Pat. No. 4,819,559 is a cellstructure only.

It is noted that U.S. Pat. No. 4,301,583 discloses a anilox roll. Theknown anilox roll comprises a structure of honeycomb cells. Two adjacentcells are connected through a straight channel. The cells and channelsform in a circumferential direction of the anilox roll a single row. Thecourse direction of the channels in a row are located at a single line.The centre point of the connected cells are positioned in a single row.The linear distribution of the fluid is allowed in a circumferentialdirection of the anilox roll in the known embodiment. The side walls ofthe channel are not arranged to allow meandering of a fluid throughout afluid distribution structure. The disclosed structure does not combine adevice for printing heavy layers of ink and a device for printingdetails, but can function only according to one operational mode.

From WO 96/40443 a engraved roll is known, having a structure fordistributing a fluid over the surface of the roll. The known structurecomprises diamond shaped cells, the cells being positioned in acircumferential direction of the roll in a single line. The cells areinterconnected through small channels. The course of the channelsextends in the circumferential direction of the roll. Side walls of thestructure as disclosed in WO 96/40443 are symmetrically positionedaround the longitudinal axis of the channel, i.e. the course of thechannel. The known channel allows linear distribution of the fluid in acircumferential direction of the roll. According to the inventionrestrictions will prevent such a linear distribution.

A restriction to be used in combination with the fluid distributionstructure can be the channel depth. By reducing the channel depth alocal change of the fluid distribution structure is obtained, which willallow reducing the droplet size of the ink to be received in the channelpart having the reduced channel depth. Such a local change can form aweak link between cells formed at both ends of the channel having thereduced depth. The channel depth can for example be reduced with at most50%, but preferably at most 30%. Because varying the channel depth willlocally influence the size of the ink droplet to be received in thechannel part, such a restriction is not preferred. In experiments by theapplicant it is shown that a local change of restrictions cooperating toallow a constant local droplet size in the structure, results in thebest printing properties.

The channel preferably has a generally flat or single level bottom. Thiswill allow the channel to receive relatively large amounts of ink overits entire length or at least a large part of its entire length. A flatbottom improves the capabilities for printing in the first operationalmode for printing heavy layers of ink.

A channel comprises channel parts that are connected to each other. Thechannel parts are arranged to receive ink droplets of relatively smallsize that are suitable for printing details. The connection between thechannel parts comprises preferably a connection of the same channeldepth as the channel parts. This will allow physical interaction betweenthe volumes of fluid received in the adjacent channel parts.

In an embodiments the channel parts have a generally constant width.This will allow transport of fluid between the channel parts in arelatively simple way. The flow of fluid between the channel parts isdiminished by changing the course of the channel. In such an embodimentthe channel lacks local congestion and/or upward pressure points. Upwardpressure points have a negative impact on printing properties since theink will be pushed out of the channel. This will prevent filling of thefluid distribution structure completely, which will diminish thefunction of the device for printing heavy layers of ink. In particularupward pressure can be the result of a blade scraping the roll. U.S.Pat. No. 4,819,558 discloses such upward pressure point formed byconverging walls, converging in a direction parallel to thecircumferential/rotational direction.

In an embodiment the restrictions are formed by side walls of thechannel. The restrictions comprise preferably at least 90%, in anembodiment at least 95%, and in an embodiment at least 98% restrictionsin the form of wall parts. A wall part will extend above the fluid levelwhen fluid is received in de structure, between the wall parts.

It is possible that wall parts forming side walls of a channel extendingperpendicular from a bottom of the channel. By application ofperpendicular side walls restricting the bottom of the channel, achannel can receive a relatively large amount of ink. The channelpreferably has a U-shaped cross-section. The channels can have a limiteddepth in respect of pyramid shaped cells, which will reduce the chanceof ink residues remaining in the channel after transferring ink onto theprinting roll. A generally flat bottom will prevent forming stagnationor upward pressure points/regions in the channel.

The anilox roll having a surface according to the invention will allowcombining the properties of an anilox roll having a cell structure of100 lines per centimeter (first operational mode) and an anilox rollhaving a cell structure of 180 line per centimeters (second operationalmode) to be combined. The invention allows a resolution up to 300-500lines per centimeter, and such an anilox roll according to the inventionwill still be able to print heavy layers of ink having desired colourintensity properties. An anilox roll will have a surface that will allowthe ink to be received more evenly distributed. Stress is reduced in theink. The ink lies calmly on the surface of the anilox roll, which willallow subsequent transfer.

Ink is received in the channel parts more easily in comparison to a cellstructure. Ink can be transferred from the surface of the anilox rollmore easily. Tensions in the ink will be reduced during transfer.Rotation of the anilox roll during the printing process will result inless scraping of the ink from the anilox roll in comparison to a cellstructure. The ink is pressed in front of the blade and is received inthe open structure of the channels. The internal stress in the ink isreduced. An advantage is that printing a heavy layer ink is possible,whilst having a grid of fine lines that allows printing details on asubstrate.

Distribution of the fluid is allowed according to one aspect of theinvention in a limited way. By limiting distribution of the fluid overthe fluid distribution structure a problem known for prior art aniloxrolls is prevented. Known anilox rolls having parallel straight channelswill allow too much distribution of the fluid, which results in notbeing able to dose the ink in proper amount, in particular for printingdetails. The restrictions according to the invention will allow suchdosing in relatively small amounts of ink.

In an embodiment wall parts of a channel part are positioned in a radialdirection from a position in the fluid distribution structure within adistance less than 120 μm, in an embodiment less than 100 μm, preferablyless than 80 μm. Every location within the fluid distribution structureis surrounded by a restriction at a relative short distance.

This will prevent linear distribution of the fluid in an efficientmanner. It is advantageous to restrict distribution of fluid in radialdirection using wall parts. A limited distribution is allowed only. Thechannel comprising channel parts does not extend linearly, but issuitably curved.

The curvature in an embodiment is a least such that straight connectionlines between locations in different channel parts are prevented. Asuitable curvature can be an angle of at least 30 degrees, in anembodiment at least 45 degrees and in an embodiment at least 90 degrees.

In an embodiment foaming is prevented by channel parts extending, andpreferably a channel having channel parts extending generally in acircumferential direction of the anilox roll. Such channels can beformed in a suitable manner as will be explained in more detailhereunder or using known techniques for forming such channels, whereinsuch channels extend adjacent to each other in a circumferentialdirection of the anilox roll.

Preferably in a longitudinal direction adjacent a first channel, asecond channel is formed. The second channel is parallel to the firstchannel. A fluid distribution structure can comprise paralleloscillating or wavy channels. Such oscillating channels can be formedparallel to each other. The channels can be separated from each other bymeans of a separation wall or side wall. In a channel a meandering flowof fluid is allowed, preferably in a circumferential direction of theanilox roll. The ink can be distributed over the anilox roll. The freepath in the channel structure is limited by restrictions according tothe invention which will allow printing of details onto a substrate dueto relatively small volumes of ink formed in the fluid distributionstructure.

A wall between the first channel and the second channel can have a widthof smaller than 4 μm, preferably in a range of 1-3 μm. Arrangements ofrelatively small walls will results in a relatively large amount ofsurface of the anilox roll that can be used for receiving fluid. Theamount of received and transferred ink in combination with the highresolution of detail is improved substantially with respect to prior artarrangements and allows functioning in both operational modes. Incombination with the perpendicular side walls extending from a bottom ofthe channel, the channel will have a relatively large volume forreceiving ink, said volume of ink being easily transferable, leavingsmall amount of ink residue, for printing details. The channels compriserestrictions that allow printing details in the image printed on thesubstrate. Restrictions are formed by wall parts of the channel. Theamount of ink that can be transferred is, when ink is combined fromdifferent channel parts, enough to allow printing of heavy layers of inkon the substrate.

To allow a meandering flow of fluid in the channel, the side walls ofthe channel can be formed anti-symmetrical with respect to the course ofthe channel. This will allow forming a wavy or oscillating pattern ofchannels. The channels have a course that follows a sinus. The course ofthe channel changes at every position and this change forms arestriction according to the invention, which allows the anilox roll tofunction according to both operational modes. The wall parts of thechannel, in this embodiment oscillating wall parts, allow a connectionbetween the ink volumes received in the channel over the length of thechannel, but do also allow disconnecting the connection between the inkvolumes as a result of curvatures in the channel course, allowingobtaining relatively small volumes of ink for printing details.

The oscillating channels can have an amplitude that is generally equalto or preferably larger than the width of the channel. This will preventthe linear distribution of fluid in the oscillating channel. A flow offluid in the channel is will force ink to follow the meandering channel,already curving at a distance from the channel side walls.

In an embodiment channels have a width in the range of 10-200 μm, in anembodiment 10-100 μm, preferably 15-80 μm.

In an embodiment a channel part is cell shaped. Cell shaped is to beinterpreted as not comprising a closed cell. It is possible that thefluid distribution structure comprises a number of separated wall partsthat surround cell shaped channel parts. The separated wall parts arefluid conducting walls that allow directing a flowing fluid in a desireddirection. Meandering distribution of the fluid in the channel formedbetween cell shaped channel parts is allowed. A linear distribution ofthe fluid is prevented. The fluid can be distributed over a large areaof the fluid distribution structure, but the distribution is diverted byrestrictions that allow meandering distribution only.

The cell shaped channel parts have at least three open connections withadjacent cell shaped channel parts. This allows distribution of thefluid received in the channel parts and allows a meanderingdistribution. The cell shaped channel parts are unlike cells accordingto the prior art, part of a channel that receives ink droplet suitablefor printing details. The connection between channel parts is arrangedto allow a relatively substantial amount of the droplet volume to movefreely between adjacent channel parts, but does not allow lineardistribution. The structure of the surface of the anilox roll accordingto the invention formed by restrictions is not a cell structure thatallows receiving fluid in the respective cells and the structureaccording to the invention does not allow unlimited linear distributionof the fluid over the surface.

The cell channel shaped channel part is in an embodiment characterisedby channel wall parts that converge towards a connecting part that formsthe connection between the first cell shaped channel part and anothercell shaped channel part. In an embodiment a channel part according tothe invention is provided only if the connection part is at least 10% ofthe channel width. 10% width guarantees sufficient distribution.

In an embodiment a cell shaped channel part has at least two connectionswithin adjacent cell shaped channel parts. This will allow thecombination of the fluid volume received in the channel parts in a firstoperational mode, because the connections allow combining the two inkvolumes, and in the second operation mode, as the connection between theconnected cells can be separated in a second operational mode, allowingtransfer of small volumes of ink. If multiple connection parts betweentwo adjacent cell shaped parts are present, the connection parts can besmaller. In an embodiment such connection parts can be smaller than 5%of the channel width. The smaller connection parts preferably do nothave a reduced channel depth.

Further a width of an open connection between channel parts ispreferably at least 40%, and more preferably at least 60% of a width ofa cell shaped channel part.

In an embodiment a cell shaped channel part has at least three adjacentcell shaped channel parts. This will allow obtaining ink volumes forprinting heavy layers of ink in a straight forward manner. In apreferred embodiment the cell shaped channel part has at least twoconnections which each adjacent cell shaped channel part. This willallow easy transfer of the ink and combination of the ink volumes duringtransfer in the first operational mode.

In an embodiment the bottom of the connection between channel parts isat the same level as bottoms of the channel parts. A restriction in theflow between the channels is reduced and is only limited by the positionof the channel walls. The channel depth is not a congestion point forthe ink, which would result in not optimally applying the properties ofthe fluid distribution structure.

The open channel structure allows a high line screen of preferably over120 lines per centimeter and in an embodiment at least 150 lines percentimeter. This allows printing in a high resolution. The openstructure allows the transfer of high volumes of ink that in prior artarrangement would only be possible if cell structures would be usedhaving relatively low line screen. The invention allows a high linescreen and printing of heavy layers of ink having a desired intensity.

The channel formed in the surface of the anilox roll extends over arelative large surface area through connections. This relative largesurface area allows collection of a large amount of ink during transfer.The connected channel parts can have a surface area of at least four orsix or even ten times larger than the surface of the cell of aniloxrolls according to the prior art.

According to an embodiment the fluid distribution structure has a grid.The grid repeats itself over the surface of the roll. The grid is formedby wall parts of the channel and channel parts formed between the wallparts. The grid forms the fluid distribution structure that allows alimited distribution of the fluid of preferably at most four times thesize of the grid. In an embodiment a linear connection between twopoints on the fluid distribution structure is limited to a length of atmost four times the grid size. The skilled person will be able todetermine a grid size. A grid size can be determined in a manner similarto prior art arrangement, for example lines per centimeter.

In an embodiment the free path, that is the length in a straight linefrom a point in the fluid distribution structure that is positionedbetween two walls in a first direction is at most four times the freepath in the second direction perpendicular to the first direction. Thesecond direction is preferably a connecting line between two generallyparallel walls or the course direction of the channel part. Thedistribution as a result of a free floating path is in this embodimentellipse shaped. The limited distribution correlates preferably with thegrid size and therefore with the length of the connection line betweentwo at least parallel side walls of two different open cells. Thelimited distribution according to an embodiment is further limited to atmost three times the grid size.

Preferably an anilox roll is provided having a channel part that is cellshaped having a combined surface area of at least 20.000 and moreparticular at least 40.000 μm². In an embodiment the combined surfacearea spreads around the complete cylinder. The combined surface area isthe accumulation of every connected open cell in that channel. Suchsurface area can be substantially larger than the surface of the cellstructure of comparable anilox rolls according to the prior art. Suchsurface areas are similar to at least four connected cells of known gridpattern (100 lines per centimeter) for anilox rolls having cells.

In an embodiment channel parts extend generally in a circumferentialdirection of the anilox roll. This will allow an open connection betweenchannel parts in a circumferential direction. This is advantageous forfilling the channel parts with the fluid. Because the channels areconnected with other channel parts in a circumferential direction, inkis received more easily in the channel in respect of anilox rolls havingcells according to prior art arrangements, while the channel part,preferably having a reduction in width of at most 40% at a connectionbetween channel parts, allows escaping of air trapped in the channelthat is receiving the fluid. This reduces the amount of foaming of theink during the printing process.

In an advantageous embodiment a structure of restrictions formed bywalls is provided having a pattern of wall parts and wall partspositioned perpendicular to the first wall part, wherein said wall partsare at least twice the size of the channel width of the channel formedbetween the wall parts. This is a particularly simple embodiment of anopen structure having a limited free path. In an advantages embodimentthe free path is at most four times the channel width.

The invention further relates to a printing apparatus. The printingapparatus comprises a printing device having a supply for a substrate tobe printing and a supply for ink, wherein the printing device comprisesan anilox roll mounted in a bearing, said anilox roll comprising atleast one of the features mentioned above.

The invention also relates to a method for forming an anilox roll. Themethod comprises supplying a cylinder for an anilox roll that has anouter surface to be tooled. The method preferably comprises providing atleast a laser source and laser engraving the outer surface of the aniloxroll. It will be clear that a person skilled in the art will be able touse future techniques that work in a similar way as a laser, forcarrying out the method according to the invention.

The method according to the invention comprises laser engraving theouter surface of the anilox roll with a laserspot that is formed withthe laser source. The laser and its laser spot are able to focus theintensity of the beam to a small position on the anilox roll. Thisallows tooling the anilox roll. The anilox roll may be used in theprinting industry.

The method according to an embodiment of the invention comprisesapplying an optical guide in the light path of the laser for enablingthe laserspot to execute a reciprocal movement on the outer surface tobe tooled. The reciprocal movement leads to a repetitive movement in theposition of the laser spot. The reciprocal movement preferably causes ashift of the laser spot on the anilox roll in a direction that is mainlyparallel to a longitudinal axis of the anilox roll. This creates theability to execute repetitive movement of the laser spot on the surfaceto be tooled, in a surprisingly simple fashion.

In an embodiment, the laser spot will mainly move with a constant speedover the surface of the roll. A generally even evaporation of surfacematerial of on the surface of the anilox roll is obtained. This allowsforming a generally uniform channel. The depth of the channel will be atgenerally a similar level throughout the formed channel. Further thechannel will have a generally U-shaped cross-section.

In an embodiment the optical guide is a crystal. The reciprocal movementis caused by supplying an varying current to the crystal. With this, adeflection in the trajectory of the laser beam may be caused, resultingin movement of the laser spot. The varying current may be a sine likecurrent, such as a well known alternating current (AC). With this, asine like reciprocal movement is generated.

Preferably, the method comprises a shift in the reciprocal movement ofthe laser spot that is at least larger than the width of the laserspotin the likewise direction. This way, it is possible to laser engrave anouter surface having a width of two or more times the width of the laserspot. The surface may be engraved in a single operation of the methodfor forming an anilox roll. The result is that laser engraving is beperformed more quickly.

It is furthermore advantageous to laser engrave the anilox roll, whilstrotating the anilox roll around a longitudinal axis of the anilox roll.In addition, the laser may be moved in a direction mainly parallel tothe longitudinal axis of the anilox roll. By this, the complete surfaceof the anilox roll may be tooled. This technique is known from the stateof the art. By applying the reciprocally moving guide, prior art methodsmay be accelerated.

It is exceptionally advantageous to apply the method using a continuouslaser. This enables the possibility to move the continuously whilereciprocally moving the laser spot over the surface. In combination withthe rotating anilox roll, which may rotate around its longitudinal axis,a wobbling track may be burned. This track is comparable to a track on aCD or DVD. The method of forming an outer surface that comprises such awobbling groove, surrounded by walls that are left unburned, mayadvantageously be applied in the printing industry. Laser engraving isused here to form a channel that extends in a rotational direction ofthe anilox roll.

A further goal of the invention is obtained by an apparatus for formingan anilox roll for use in a printing process, comprising a supportingunit for supporting the cylinder shaped anilox roll and for rotating theanilox roll around a longitudinal axis. According to an aspect of theinvention, the apparatus comprises an engraving unit that is arrangedfor parallel movement with respect to a cylinder-axis of the anilox rollfor engraving a structure on the outer surface of the anilox roll,especially in combination with a rotating anilox roll. The apparatusalso comprises a driving unit for driving engraving settings of theengraving unit. The engraving settings are the driving parameters forthe engraving, with which the engraving can be influenced. The personskilled in the art will understand how to set the engraving.

Advantageously, the engraving unit comprises at least a laser for laserengraving the outer surface of the anilox roll with a laser spot. Atleast one goal is obtained when the engraving unit further comprises anoptical guide for adjusting the light path of the laser, and morespecifically for moving the laser spot in a repetitive or reciprocalway. With this, an additional shift of the laser spot is possible. Theposition to be tooled may also be chosen this way. By using an opticalguide, it is possible to realize an additional shift of the spot,allowing quick and small shifts. More specifically, these shifts may berepetitive.

In a further advantageous embodiment, the optical guide is a deflector.A deflector, such as a crystal may be used, with which the trajectory ofthe laser, and thus the position of the laser spot may be adjusted, morespecifically shifted. The deflector may be controlled in a fast andaccurate manner. The person skilled in the art will be familiar with thedifferent deflectors for creating a repetitive transition of the laserspot. In an advantageous embodiment, the crystal may be connectable to apower supply, more specifically a drivable or controllable supply,wherein the voltage supplied is in proportion with a certain deflectionand more specifically a shift of the laser spot.

In an embodiment, the crystal may be arranged for deflecting theentering laser beam in a voltage depending way.

In another advantageous embodiment, the engraving unit comprises anoptical guide that is positioned in the light trajectory of the laser,wherein the guide is movably connected to the engraving unit. Thisenables the movement of the laser spot on the surface of the aniloxroll, additional to the movement of the engraving unit as a whole. Theextra movement is superimposed.

It is especially advantageous to connect the optical guide to theengraving unit by means of a movement unit, wherein the movement unit isarranged for enabling the laserspot to execute a reciprocal movement.This way, a reciprocal and repetitive movement of the laser spot may beused for forming a regular structure on the anilox roll. This regularstructure may be obtained by engraving a rotating anilox roll, andadditionally move the laser in a longitudinal direction along the roll.The structure thus formed, is different from the lined structure formedin a usual manner.

The reciprocal movement preferably causes a movement of the laser spotin a direction mainly parallel to the cylinder axis. With this, a largersurface may be tooled in a single labour-step. Preferably, the shift isat least larger than a width of the laser spot in the likewisedirection. This allows tooling an area having a width of at least twicethe spot size. Also, with this a wave like motion may be obtained whenthe reciprocal movement is combined with a rotation of the aniloxrolaround its longitudinal axis.

According to the invention, the laser may be a continuous laser.Especially in combination with a rotating anilox roll and a reciprocallymoving guide, a track or channel is formed on the anilox roll. The trackhas a wobble. The driving unit is preferably connected to the supportingunit and to the movement unit. The driving unit may be arranged forrotating the anilox roll during the laser engraving with a reciprocalmoving laser spot. This enables the manufacturing of a novel aniloxroll, having advantageous properties for transferring ink. The ink maybe easily absorbed temporarily in the wobbling channels.

It is advantageous to provide the engraving with an objective lens. Thelens is able to focus the laser. The lens may be the optical guide thatperforms a reciprocal movement.

It is possible to provide the engraving unit with two lasers or morelasers and/or with one or more beam-splitters. This way multiplechannels may be provided in the anilox roll simultaneously.

In an preferred embodiment, the reciprocal movement leads to a shift ofthe laser spot of at least 20 μm. This small shift may be sufficient forcreating a wobble in the channel on the tooled surface of the aniloxroll.

Although the invention is described and will be described with respectto preferred embodiments, it will be clear that within the scope of theinvention, multiple and different embodiments are possible. It is a goalof this application to protect the embodiments described, theembodiments indicated by the claims, as well as equivalents thereof. Theperson skilled in the art will—now that the advantages of the inventionare experimentally known—be able to construct different embodiments. Itis an intention of the inventor to also protect these embodiments withthis application.

More specifically, the skilled person is able to form restrictions onthe surface of an anilox roll in accordance with the disclosure in thisapplication that allows obtaining one or more of the advantages.Functional protection should therefore be allowed.

In the above, as well as in the following description, aspects of theinvention are described and advantages of the measures are described.The inventor intends to protect all the mentioned and unmentionedadvantages that the invention has with respect to the state of the art,using this application and/or divisional applications.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described by reference to the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic side view of a printing apparatus for aflexographic process;

FIGS. 2 a and b are detailed views of a surface of an engraved aniloxroll according to the state of the art.

FIG. 3 a-h are detailed views of embodiments of an outer surface of ananilox roll according to the present invention.

FIG. 4 is a detail of a part of the canal section of an anilox rollaccording to the embodiment of FIG. 3 b, and

FIG. 5 is a schematic view of an embodiment of a engraving deviceaccording to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic side view of a part of a printing apparatus 1used for example in a flexo process. The printing apparatus 1 may bepart of a series of printing apparatuses for printing with differentinks or printing with various techniques. The person skilled in the artwill be familiar with the different embodiments of a printing apparatus1. The printing apparatus 1 is suitable and arranged for applying ink toa substrate in a desired pattern.

In the embodiment shown the printing apparatus 1 comprises a fountainroll 2 which is partly emerged in an ink fountain 4 comprising a certainamount of ink 3. The fountain roll is rotatable, and the outer surfaceof the fountain roll may be a rubber coating.

Next to the fountain roll 2 a rotatable metering roll or anilox roll 5is positioned, wherein the longitudinal axis of the anilox roll 5 ispositioned parallel to the longitudinal axis of the fountain roll. Thisallows forming a contact point or contact line 6. The rolls 2 and 5 arein contact, or almost in contact with each other. Adjacent acircumferential side of the metering roll, a blade 7 is positioned overat least a part of the length of the metering roll. In line with thelongitudinal axis of the metering roll 5, a rotatable printing cylinder9 is positioned. The printing cylinder comprises elevations andrecesses, the elevations forming a negative of the image to be printed.

The elevations and recesses determine the operational mode for theanilox roll 5. When the image contains details, ink in the form ofrelatively small drop sizes should be transferred from the anilox rollonto the substrate, whilst for printing heavy layers of ink relativelylarge drop sizes are to be transferred.

The substrate 13 or the product to be printed may be positioned next toa circumferential side of the printing cylinder. The substrate ismovable in a lengthwise direction. A rotatable impressing roll 11 ispositioned next to a side of the printing roll 9, wherein the printingroll 9 and the impressing roll 11 are positioned on both sides of thesubstrate.

In the figure an example of a substrate 13 is shown. It will be obviousthat different sorts of substrates 13 may be printed. The person skilledin the art will be able to adapt the printing apparatus to the substrateto be printed.

An operational method of the apparatus shown will be described next.When the apparatus is operated, the fountain roll 2 will be driven,resulting in a rotation of the fountain roll 2 such that the outersurface of the roll will move through the ink 3 of the ink fountain 4.The outer surface of the fountain roll can comprise a rubber layer, theink will be absorbed and will be transported in the direction of theanilox roll 5, which is rotating in an opposite direction compared tothe fountain roll. Near the contact point 6, the ink will be transferredfrom the fountain roll 2 to the anilox roll 5. The surface of the aniloxis provided with a structure for absorbing ink. The structure isdescribed in more detail in FIG. 2.

The anilox roll 5 will absorb a certain amount of ink of the fountainroll 2. The blade 7 ensures that an excess of ink is scraped off, suchthat the anilox roll 5 absorbs and retains with a suitable amount ofink. Next, the ink will be transferred onto the printing roll 9. A finelayer of ink is transferred onto the elevations of the printing roll 9.Compared to the anilox roll 5, the printing roll 9 is rotating inopposite direction. The printing roll 5 will continue to rotate and willapply the image to the substrate 13. The impression roll 11 supports thesubstrate during the printing process.

Other configurations are also possible. The apparatus may be providedwith a closed ink fountain 4 comprising an ink supply and an ink drain.It is also possible that multiple blades 7 are provided. The descriptionof the configuration is only meant to be an example. It may be obviousthat multiple configurations of the anilox roll 5 are possible, withoutdiverting from the invention.

FIG. 2 a shows a detailed view of a surface of an anilox roll 5. Thesurface structure shown is known from prior art. The anilox roll 5 isprovided with a structure 14, which may be formed of a plurality ofregularly positioned cells 15. The cells 15 are formed by recesses inthe anilox roll 5. The cells 15 are separated from each other by meansof side walls 17 having a width w1. According to the state of the artthe width w1 may be 10-80 μm. The side walls ensure that the ink cannotmove from one cell to another. If ink is provided onto the surface ofthe anilox roll having the surface structure 14, side walls 17 willextend above the ink level. Ink will be inserted in cells 15. Excess inkwill be removed by blade 7.

The cells have a global size h in the order of 10-80 μm. Each cell has adepth (not shown). Each cell has a certain volume. The ink volumecorresponds with the ink droplet to be transferred onto the printingroll and the substrate.

In the embodiment shown the cells are hexagonally shaped, and the cellsare positioned in a honeycomb like structure. The distance c between thecentre point of two neighbouring cells, wherein the distance is measuredperpendicular to the rotating direction of the roll, determines the linescreen of the anilox roll. Known line screens for prior art cell-likesurface structures are 100, 120, 140, 180 lines per cm.

FIG. 2 b shows another embodiment of an outer surface of an anilox rollaccording to the state of the art. In this embodiment channels 18 areapplied along an outer surface of the metering roll. The channels have awidth h (15-80 μm) and are separated from each other by means of a wall19 having a thickness t. The longitudinal direction of the channels ispositioned with an angle α with respect to the direction of rotation Rof the metering roll. Such an embodiment is suitable for applying ink tothe substrate in a smooth fashion. It is clear that the channels arestraight lines and thus that there is no restriction in the spreading ofink in the channel.

Anilox rolls presently known do not individually meet the criteria thatare currently set in the printing industry. Therefore it is necessary inmany applications that different anilox rolls are used, which issomething that slows down the printing process and which makes theprinting process labour intensive time consuming and expensive.

FIG. 3 a shows a first embodiment of an anilox roll according to thepresent invention. FIG. 3 a shows a view of the rolling surface 100 ofan anilox roll wherein a fluid distribution structure is applied. Thefluid distribution structure is shown more specifically by means of wallparts of channels that are formed in the structure. The wall parts arerepeatedly indicated with lines. The “void” parts in FIG. 3 a arerecesses in the rolling surface, which may for example be formed bymeans of laser and graving and/or laser evaporation.

The part of the rolling surface 100 that is shown in FIG. 3 a isprovided with a pattern, which is formed by two wall parts 21, 22 thatare positioned with an angle with respect to each other. The wall partsform dams or restrictions and have a thickness t. The wall parts 21, 22are surrounded by a channel 20 which spreads over the outer surface ofthe anilox roll. The channel is arranged for absorbing mass, morespecifically ink. The ink may be taken up in the formed channel 20 andmay spread over the outer surface, wherein the restrictions ensure thatthe ability to flow is limited.

In an embodiment the first restrictions 22 are placed with an angle ofabout 90 degrees with respect to the second restrictions 21. The firstrestrictions 21 are furthermore positioned with an angle γ with respectto the direction of rotation R of the anilox roll. Preferably γ is equalto 0 degrees. The second restrictions are positioned longitudinally fromthe first restriction, and the restrictions are positioned with an angleof 90 degrees with respect to each other. Other angles are of courseimaginable. In this fashion a regular pattern is obtained. In anembodiment the pattern may form a herringbone pattern.

Preferably the pattern of the anilox roll is formed in such a mannerthat an ink volume only has a limited free path or pathway distance,measured from an arbitrary point in the absorption surface 20. Thepathway distance is defined as a distance that an ink part may move in arandom radial direction starting from a random point in a channel untila wall is reached. Preferably the free path is smaller than 150 μm, andin the embodiment shown smaller than 100 μm. Preferably the free path isless than 50 μm. The free path ensures that the ink can freely flowalong a certain, but restricted length. Due to the fact that the freepath is limited, a resistance force is applied to the ink such that theink cannot flow freely over a too large part of the roll. Due to thefact that the restrictions are positioned at a relatively short distancefrom each other, a large distribution of ink is impossible.Surprisingly, in this fashion an anilox roll is obtained that on the onehand has an open structure, but wherein on the other hand cells, in thiscase open cells can be recognized. Printing tests with such an aniloxroll have shown that such a structure allow printing of heavy layerswith sufficient color intensity as well as printing of small detailedstructures. According to the state of the art, this result was onlyobtainable by printing in two steps, more specifically by first using ananilox roll with a small line screen, and then using an anilox roll witha large line screen, or vice versa.

In an embodiment the restrictions have a width t which is smaller than 8μm. Preferably the restrictions have a width that is smaller than 5 μm.Even more preferably the restrictions have a width t that is between 2and 3 μm. In this fashion the walls only form a very small part of thetotal surface of the circumference of the anilox roll. It will be clearfor the person skilled in the art that the wall parts according to thepresent invention function primarily as restrictions against freedistribution of ink, when the ink is present between the walls.

The location of the restrictions allows forming open connections in thestructure on the outer surface of the anilox rolls. The ink maydistribute well over the anilox roll, especially when the ink is takenup in the channel. The restrictions are placed in a way to ensure thatthe ink cannot freely flow, especially when the ink is being released.The wall parts form restrictions on the anilox roll and ensure that theink is kept in place on the anilox roll. The presence of the largeabsorption surface 20 ensures that the anilox roll according to thepresent invention is able to take up a large volume of ink. In addition,the restrictions enable that the ink may be taken up well from thefountain roll. The positioning of the restrictions is such that inkreceived in the fluid distribution structure can freely, but limited,distribute over the anilox roll, such that generally a small film layerof ink is provided on the anilox roll.

Additionally, unlimited distribution of ink is prevented by therestrictions, since the restrictions form natural barriers against inkflow. Additionally, the structure of the anilox roll ensures thattransfer of ink onto the printing roll is possible in multipleoperational modes. Negative parts of the printing roll are provided witha dosed amount of ink, wherein also the detailed parts of the negativeare provided with the suitable amount of ink.

It is therefore possible with an anilox roll according to the presentinvention to obtain a good color intensity and heavy layers, as well asfine structures in line art. Therefore it is not necessary anymore inspecific cases wherein both full colour intensity as well as details areimportant, to switch the anilox roll. Only one anilox is needed forprinting both heavy layers and fine details.

Another advantage of the anilox roll according tot the presentinvention, is that it needs to be cleaned less often. Anilox rollsaccording to the state of the art have large amounts of walls 17, 19. Inaddition, the walls 17, 19 take up a large amount of space with respectto the total available inking surface. According to the presentinvention the wall parts take up less than 10%, in an embodiment lessthan 5% or 3%, preferably less than 2%, of the total surface of theanilox roll.

To transfer a suitable amount of ink, the cells 15 and channels 18according to the state of the art have a relatively large depth. Often,the depth of the cell or the channel is larger than the width thereof.This results in the fact that it is hard for the ink to get out of thecell or the channel, and eventually ink residues will accumulate andblock the cell or channel. The anilox rolls then need to be cleaned.This is a hard and tedious job, which is also due to the fact that thecells and channels have a relatively large depth. In addition the aniloxrolls may be damaged easily during cleaning.

In the anilox rolls according to the present invention this problem isless relevant. Due to the fact that a larger absorption surface 20 forink is present, a smaller depth will be needed to transfer the rightamount of ink. In addition the restrictions are positioned at arelatively large distance with respect to each other. This ensures thattransfer of the ink is relatively easy, such that accumulation of ink inthe anilox roll according to the present invention is less likely tohappen. An additional advantage of the relatively large distance betweenthe restrictions, and the relatively smaller depth of the anilox roll,is that the surface structure can be reached more easily for cleaningthereof.

In an embodiment of the present invention, as shown in FIG. 3 b,meandering channels 24 are provided, having uniform walls 25. It isrelatively easy to form this embodiment. The meandering channels mayhave the form of a wave, more specifically a sine wave, see FIG. 4,wherein in succession a turn in the one direction is alternated by aturn in the other direction. With reference to FIG. 4, the walls have atop 32 and a bottom 31, wherein the walls have an amplitude a andwherein the walls oscillate around a base line 30.

Preferably the base line 30 of the sinusoid, is positioned parallel tothe direction of rotation R of the anilox roll. The course of themeandering channel 24 follows a sinusoid.

Due to the fact that in a preferred embodiment the amplitude of the waveis larger than the width of the channel, a channel is obtained withlimited possibilities for spreading or distributing of the fluidreceived in the structure. In this application, the term free path isused. Free path refers to a radial expansion from any arbitrary point inthe formed channel. In the sinusoid channel shown, the free path islimited to a maximum of one wave length. By limiting the free or radialdistribution, it is possible for the ink to be absorbed in the channelson the outer side of the anilox roll. The limited distribution resultsin a decreased tension in the ink that is absorbed on and supplied fromthe anilox roll when in use. The volume of the channel parts on theouter surface of the anilox roll is relatively large compared to stateof the art volumes that are obtained using grid patterns of closed cellshaving a large line screen. With the anilox roll according to thepresent invention it is therefore possible to approach and/or improvethe properties of the large line screen anilox rolls.

However, the pattern of the anilox roll according to the presentinvention also has a limitation of the direct spreading. With this, itis possible to also apply the details on the substrate during theprinting. According to the state of the art, this was only possibleusing anilox rolls having a relatively small line screen. The aniloxroll according to the present invention combines these two properties(heavy layer and small detail printing) and thus leads to a reduction inthe amount of printing steps needed in the printing process.

The limitation in the spreading is obtained due to the fact that wallparts 25 always create somewhat limited channel parts that are on theother hand connected with each other via (indirect) connections. Thechannel parts according to the invention are limited due to the factthat distribution in a straight line in between the wall parts 25 issmaller than the indirect or curved distribution.

In the example of FIG. 3 b the wave length is comparable to the gridsize of the pattern. The grid size and the channel width are comparable.Preferably the wave length is smaller than four times the grid size,preferably smaller than two times the grid size. Due to the fact thatthe grid size and the wave length are comparable, in fact each time acell like pattern is obtained that is comparable to a honeycomb patternaccording to the state of the art. According to the invention, however,these cells are connected in a limited way with each other and separateconnections are formed by removing closing wall parts.

The fluid can be distributed over a large part of the surface of theanilox roll if the followed path meanders over the surface.

The wave length may be 80 μm for example, whilst the grid size is equalto approximately 30 μm. The anilox roll according to the presentinvention, having these dimensions, combines the properties of aniloxrolls having a large and small line screen, i.e. heavy layers of ink(first operational mode) and detail printing (second operational mode)possibilities.

FIG. 3 b shows an embodiment, wherein two walls that are situated nextto each other are positioned at a distance from each other. Walls 26, 27that are positioned next to each other have a distance d that is equalto two times the amplitude a of the sinusoid. Dips 26 of one wall goinside with tops 27 of the neighbouring wall. This embodiment ensuresthat the ink parts obtain a maximum free path. The structure/the patternprevents that the mass to be taken up between the wall parts can easilyspread, and more specifically that during the supply of ink by theanilox roll a large mass of ink can gather for supply. Curvedconnections between channel parts are possible. With this, theaforementioned gathering becomes possible, but only in a certain smallamount. With this, relatively large volumes of mass may be transferred.Additionally it is possible, such as shown in FIG. 3 c, to position thechannels and the walls with angle β with respect to the direction ofrotation (or circumferential direction) R. Especially for printing heavylayers of ink this is a beneficial embodiment.

FIG. 3 d shows another embodiment, wherein different restrictions 51,52, 53, 55 are placed in such a fashion, that a regular pattern isformed. The line shaped restrictions 51, 52, 55 are positioned in atriangular fashion, wherein the corner parts of the triangle are formedby cross shaped restrictions 53. In between the cross shapedrestrictions 53 and the ends of the line shaped restrictions 51, 52, 55recesses are present. An ink particle can freely flow between differenttriangular channel parts 54. The free flow in a linear of straight lineis limited. The walls form dams to restrict the spreading of mass in thechannel parts. In addition, the walls form dams against the accumulationor concentration of ink, for example when the ink has being supplied.

The restriction in the shape of the cross shaped wall part 53 preferablyhas a size that blocks the flow of fluid along wall part 51, but allowsdiversion thereof. By increasing wall part 53 a larger barrier isformed. The distance between an end of wall part 51 or 52 and the crossshaped wall part does not change by this, however. The size of theconnection part therefore stays the same.

The size of the connection part 49 is preferably equal to at least 10%of the length of wall part 52. By this the cell shaped channel parts 47,48 that are positioned in opposite sides of wall part 52 have an openconnection with each other. In addition two connections are formedbetween those cell shaped parts. In the first operational modus it isrelatively easy to obtain a relatively large drop size of ink due to thefact that both cell shaped channel parts 47, 48 supply the ink.

The capacity of cell shaped channel parts 47, 48 is approximately equalto the relatively small drop size that is desired for printing detailsand corresponds to the drop size that is desired for printing details inthe state of the art, such as for example 180 lines per centimeteranilox rolls.

This pattern ensures that the ink may be absorbed well in the aniloxroll, and that the ink may be supplied well to the printing roll.Additionally this embodiment ensures that the ink has sufficient freedomto flow, and nevertheless that a film layer is present on the aniloxroll.

Likewise, FIG. 3 b is an example of a meandering channel since flow offluid along a large part of the surface of the anilox roll is possible,because the cell shaped channel parts are connected with each other. Byflowing along wall parts 51, 52 fluid is able to reach other cell shapedchannel parts. Exactly this property ensures that the anilox roll isable to combine the printing properties of both the first and secondmodes of operation.

The embodiments of FIGS. 3 a to 3 d have a fluid distribution structurethat is formed on the surface of the anilox roll, wherein the formedchannels mainly have a similar depth. With this the volume size of fluidin the channels will not be disturbed locally and thus the fluid willremain more easily distributed over the outer surface than in the stateof the art.

FIG. 3 e shows a further embodiment according to an aspect of theinvention. The embodiment shown comprises a channel 301, which has wallparts 302, 302′. The channel 301 has a width w2. The wall parts arepositioned next to each other in a relative parallel oscillatingfashion. In this way a sinusoid like oscillating channel is obtained.The wall parts are placed at such a distance from each other, that thetop 351 and dip 352 that are closest to the centre of the channel 301,are spaced with an interval t. The interval suggests that straight lineddistribution of the fluid is possible. It has turned out however thatwhen the interval t is relatively small, this straight lineddistribution is prevented. The wall parts form restrictions thatdetermine a coarse of the formed channel. The formed channel meandersover the surface of the anilox roll.

The profile of the flow in the channel will mainly be the same in thedifferent channel parts, which means that the profile of the flow willbe the same in those parts of the channel that run in differentdirections. However, the direction of the profile of flow, and hence theflow, will be different in neighboring channel parts. The flow has nopossibilities to develop in a straight line, in the direction ofrotation R. The walls guide the flow in such a fashion that the flow canonly meander over the channel.

Preferably the interval t is small compared to the width w2 of thechannel. Preferably the interval t is smaller than 10% of the width w2of the channel, and even more preferably smaller than 5% of the width ofthe channel.

FIG. 3 f shows an embodiment of a channel 401. The channel comprisessawtooth shaped walls 403, 403′. In the channel 401 different channelparts 405, 407, 409 are visible, each having their respective course406, 408, 410. A course 408 of the channel part 407 is positioned at anangle with respect to the course 406 of a neighbouring channel part 405.In the embodiment shown the angle is approximately equal to 90 degrees,but it is also possible to use other angles. By positioning the channelparts at an angle with respect to each other, the straight lineddistribution of fluid in the channel is prevented. On the other hand,meandering flow in the channel 401 is possible. The walls 403, 403′ areplaced in such a fashion that these walls guide the flow in a meanderingfashion. Straight line distribution of the fluid is prevented by thewalls.

FIG. 3 g shows a cross section of a channel 501 according to anembodiment of the invention. The bottom 503 of the channel is mainlyflat. The walls 502, 502′ are mainly positioned perpendicular to thebottom 503. In this way a relatively large amount of fluid can beabsorbed in the channel. Preferably the width of the channel is largewith respect to the height of the channel. In this way a large volume offluid can be absorbed in the channel, and in this way it is alsopossible to supply the amount of fluid relatively easy. There is only arelatively small amount of fluid that will remain in the channel duringthe printing of the substrate.

Additionally, it is possible that the embodiment shown in FIG. 3 gconcerns a cell shaped channel and a channel according to an aspect ofthe invention. The bottom of the cell and the bottom of the channel aremainly positioned on the same level. This improves the flow of fluidbetween cells via the channels. In this way the channels preventcongestion or upward pressure in the fluid. Upward pressure in the fluidcan be the result of the bottom of the (connecting) channel beingpositioned higher than the bottom of the cell.

FIG. 3 h shows a channel 600 having channel parts 601-605. The channel600 is part of the fluid distribution structure for receiving,distributing over the anilox roll, as well as transferring the fluidonto a subsequent printing roll. The channel 600 is arranged fordistribution and guiding the fluid over the fluid distributionstructure. The meandering channel 600 which is shown here forms a heavylayer printing unit in the fluid distribution structure. The channel 600comprises a detail printing unit that is formed in the meanderingchannel 600 by means of channel parts 601-605. The channel parts 601-605each have a droplet volume that is suitable for detailed printing.Neighbouring channel parts are positioned at an angle with respect toeach other for preventing straight lined distribution of the fluid in acourse of the channel, as well as permitting meandering distribution ofthe fluid in the channel 600.

FIG. 4 shows in detail a restriction 33 according to an embodiment ofthe invention. In the embodiment shown in FIG. 3 b the amplitude of thewave is larger than the width between two walls. The wall itself has asize of approximately 1-4 micrometers. The channel according to FIG. 3 bhas a width in between 10 and 150 micrometers, more preferably between20 and 100 micrometers, and even more preferably between 30 and 80micrometers. The wave can have an amplitude of at least approximately 50micrometers. According to the invention an open structure is used forconsiderably reducing the size of the wall parts in comparison with thestate of the art. This leads to a further increase of the surface thatis available for receiving ink and for transferring ink by means of theouter surface of the anilox roll.

An open structure according to the invention can be characterised bylarger surfaces of channel parts between wall parts that are formed onthe outer surface of the anilox roll. The channel parts are connectedwith other large surfaces by means of connections that are provided inbetween the wall parts. Although a straight connection is preferablyprevented, a limited, meandering connection is possible.

The pattern according to the invention and more specifically the patternaccording to FIG. 3 b reduces the amount of foaming that occurs in theanilox roll. Related to this is the fact that the channel parts and morespecifically the channels are able to take up a mass, and morespecifically ink, more easily. The rotation of the anilox roll accordingto FIG. 3 b is mainly parallel to the base of the sinusoid, andtherefore the air in the open channel parts can be driven out of thatchannel part because of the relatively open structure according to theinvention.

Of course the invention is not limited to sine-like wave form channels.The channel and/or the walls may also have a sawtooth shape or any otherrepetitive pattern.

In an embodiment of the invention, the oscillating wall parts may show aphase difference with respect to each other. In this way each time astaggered pattern of wall parts is obtained. With this it is alsopossible to obtain the advantage according to the present invention.

FIG. 5 shows a schematic view of an apparatus for forming the structurein an anilox roll according to an embodiment of the invention. Here alaser is used 60. The laser is part of an engraving unit 61. Theengraving unit is positioned along the longitudinal axis 62 of theanilox roll 63. The anilox roll 63 is only shown schematically. Thefigure is not drawn to scale. The engraving unit is positioned on aframe (not shown), and the frame enables movement of the engraving unitalong the anilox roll 63 according to arrow 62. Suitable guiding meanssuch as a guiding track may be applied.

The anilox roll 63 is positioned in a container that is supported onbearings and connected to the frame. In this way the anilox roll is ableto rotate around the longitudinal axis 62 according to arrow 64. Thecombination of both rotation around the axis 62, as well as movementalong the axis 62 enables tooling by engraving of the complete outersurface with the laser. The constructions for manufacturing, morespecifically engraving the anilox roll according to the state of the artusing these movements, enable tooling with accuracies of less than 1micrometer. This amongst others enables that wall parts according to theembodiments of the invention are formed having a size of less than 5micrometers. The method allows forming channels on the surface of theanilox roll. Material in the channels is evaporated, whilst the wallparts remain.

The laser beam can be concentrated in a spot 69 on the outer surface 70of the anilox roll 63 by means of known optical guides 65-68, which inthis embodiment are formed by four corner mirrors. At the position wherethe spot is formed a certain amount of heat is concentrated such that apiece of material of the outer surface of the anilox roll willevaporate. This material may be a ceramic composition, such as achromium oxide. A person skilled in the art will be familiar with thedifferent compositions and/or compounds.

By focusing the spot it is possible to evaporate a part of the outersurface of the anilox roll. In a preferred embodiment of the invention acontinuous laser 60 is used. Synchronizing the pulses of the laser withrotational and longitudinal movements is more continuous. Morespecifically, it is possible to form a continuous track of evaporatedmaterial on the aniloxrol 63 by using a continuous laser together withcontinuous movements of the roll and/or engraving unit, thereby forminga channel. It is possible to form a continuous track at a high speed.The speed is limited by the power of the laser only.

In a further embodiment of the invention, the beam 71 of the laser 60 isinfluenced by an optical guide in the trajectory between the laser 60and the spot 69. The optical guide 72 may enforce a reciprocal movement73 of the spot over the surface to be engraved. As a result, the spotwill repeatedly execute an identical movement, preferably with acontinuous speed. This movement, together with the rotation of theanilox roll, may lead to a continuously changing location of the spot.Preferably, the reciprocal movement results in a shift 73 of the spot ina direction that is parallel to the longitudinal axis of the aniloxroll. Such a change in combination with a continuous laser may forexample be used for forming a pattern of channels according to FIG. 3 b.

Preferably, the reciprocal movement is a sine or wavelike movement. Themovement may be governed mechanically or electronically. In a preferredembodiment shown in FIG. 5, a combination of a crystal 74 on the onehand, and a voltage supplied by a power supply 75 on the other hand, isused. The voltage is supplied to the crystal. The optical guide 72 enmore specifically the crystal 74 will function as a generation devicefor the reciprocal movement of the laser spot. A voltage is supplied tothe crystal 74 for causing a change in the trajectory of the beam, morespecifically in an eventual shift of the spot. The voltage supplied is,for instance, repetitive, resulting in the movement of the spot alsobeing repetitive. A control unit 76 is, for example, provided in theelectrical connection between the crystal 72 and the supply 75. Thecontrol unit is capable of adjusting the voltage supplied. The controlunit may be connected to an external controller for synchronizing thecrystal voltage with the rotation 64 of the anilox roll 63 and movement62 along the anilox roll 63 of the engraving unit as a whole.

The change in voltage may be synchronized with the rotation of theanilox roll. The change in voltage is for example characterized byparameters such as amplitude and frequency. These two parameters may berelated to the amount of shift and the repetition of the reciprocalmovement, respectively.

In the embodiment shown, a tellurium dioxide crystal 74 may be used, forexample. The crystal functions as a deflector. By changing the voltagebetween 0 V and 10 V, transmission properties of the crystal change. Thecrystal mentioned functions amongst others at 1064 nm.

Other embodiments of generator devices and optical guides are alsopossible. It is also possible to make use of a moving mirror. In anotherembodiment, an interference effect may be used for generating thereciprocal movement of the spot.

Another technique that is known to make use of such a wobbling of achannel formed on an outer surface, is a technique for forming DVD's.The inventor is aware that a technique known in this technical field maybe used for forming such a pattern on an outer surface.

Variations on the embodiments of the different profiles are imaginable,without diverting from the main notion of the invention. It may be clearthat the invention is described by using preferred embodiments. Theinvention is not intended to be limited to these embodiments.

According to a further aspect the following clauses are provided. Clause1, a method for forming an anilox roll, comprising supplying a cylinderof the anilox roll that has an outer surface to be tooled, supplying atleast a laser source and laser engraving the outer surface of the aniloxroll with a laser spot that is formed by a laser source for obtaining atooled anilox roll, wherein the method further comprises applying anoptical guide in the light path of the laser for enabling the laser spotto move reciprocally on the outer surface to be tooled.

Clause 2: a method according to clause 1, wherein the laser spotgenerally moves with a constant speed over the outer surface of theanilox roll. Clause 3, a method according to clause 1 or 2, wherein thereciprocal movement causes a shift of the laser spot on the anilox rollin a direction that is mainly parallel to a longitudinal axis of theanilox roll. Clause 4: Method according to any one of the clauses 1, 2or 3, wherein the shift is at least larger than the width of the laserspot in the likewise direction. Clause 5: Method according to any one ofthe preceding clauses, wherein the step of laser engraving furthercomprises rotating the anilox roll around a longitudinal axis of theanilox roll, as well as moving the laser in a direction mainly parallelto the longitudinal axis of the anilox roll.

Clause 6: Method according to any one of the preceding clauses, whereinthe laser source is a continuous laser source, wherein a channel isformed on the outer surface of the anilox roll due to the laserengraving, wherein the channel extends in a rotational direction of theanilox roll.

Clause 7: Apparatus for forming an anilox roll to be used in a printingprocess, comprising a supporting unit for supporting the cylinder shapedanilox roll and for rotating the anilox roll around a longitudinal axis;an engraving unit that is arranged for parallel movement with respect toa cylinder-axis of the anilox roll for engraving a structure on theouter surface of the anilox roll, and a driving unit for driving theengraving settings of the engraving unit, wherein the engraving unitcomprises at least a laser source for laser engraving the outer surfaceof the anilox roll with a laser spot, wherein the engraving unit furthercomprises an optical guide for moving the laser spot in a repetitiveway. Clause 8: Apparatus according to clause 7, wherein the opticalguide is arranged for moving the laser spot over the outer surface ofthe anilox roll with a generally constant speed. Clause 9: Apparatusaccording to clause 7 or 8, wherein the optical guide is a deflector.Clause 10: Apparatus according to any one of the clauses 7, 8 or 9,wherein the optical guide comprises a crystal, that is connectable to apower supply, wherein the crystal is arranged for deflecting theentering laser beam in dependence of an applied voltage. Clause 11:Apparatus according to any one of the clauses 7-10, wherein the opticalguide is movably connected to the engraving unit. Clause 12: Apparatusaccording to clause 11, wherein the optical guide is connected to theengraving unit by means of a movement unit, and wherein the movementunit is arranged for enabling the laser spot to move reciprocally.Clause 13: Apparatus according to any one of the clauses 7-12, whereinthe repetitive shift comprises a movement of the laser spot in adirection mainly parallel to the cylinder axis. Clause 14: Apparatusaccording to any one of the clauses 7-13, wherein the shift is at leastlarger then a width of the laser spot in the likewise direction. Clause15: Apparatus according to any one of the clauses 7-14, wherein thereciprocal movement of the laser spot is at least 20 μm. Clause 16:Apparatus according to any one of the clauses 7-15, wherein the lasersource is a continuous laser source, wherein the driving unit isconnected to the supporting unit and to the movement unit, and whereinthe driving unit is arranged for rotating the anilox roll during thelaser engraving with a reciprocal moving spot. Clause 17: Apparatusaccording to any one of the clauses 7-16, wherein the engraving unitcomprises an objective lens.

The invention claimed is:
 1. An anilox roll adapted for use with aprinting apparatus to transfer a fluid, such as an ink, to a printingroll, comprising: a cylinder having a surface, wherein the surfaceincludes a fluid distribution structure for receiving the fluid,distributing the fluid over the cylinder and transferring the fluid,wherein the fluid distribution structure is arranged to transfer in afirst operational mode for printing heavy layers of ink a relativelylarge fluid droplet and in a second operational mode for printingdetails a relatively small fluid droplet by a combination ofrestrictions in the fluid distribution structure, wherein the fluiddistribution structure includes at least one channel formed as acontinuous track in the surface for distributing the fluid over thefluid distribution structure, the at least one channel extendinggenerally both in a circumferential direction of the anilox roll andbeing angled relative to said circumferential direction such as to beengraved on the complete surface, the at least one channel having acourse and opposite channel walls positioned next to each other in arelative parallel oscillating fashion such that the course of saidchannel is meandering over the surface and both the course of thechannel and the channel walls have the form of a wave with a repetitivepattern and the channel has a constant channel width between 10 and 150μm in a direction parallel to an axis of rotation of said anilox roll,the meandering channel having a wavelength that is smaller than 4 timesthe channel width.
 2. The anilox roll according to claim 1, wherein themeandering channel has an amplitude that is either generally equal to orlarger than the channel width.
 3. The anilox roll according to claim 1,wherein the channel has a generally flat bottom having a generally equalchannel depth, wherein the bottom has a substantially constant heightlevel difference with respect to the surface of the anilox roll.
 4. Theanilox roll according to claim 1, wherein the channel wall between thechannel and the further channel has a channel wall width which channelwall width is smaller than 4 μm.
 5. The anilox roll according to claim4, wherein the channel wall width is in the range of 1-3 μm.
 6. Theanilox roll according to claim 1, wherein the channel width is between20 and 100 μm.
 7. The anilox roll according to claim 6, wherein thechannel width is between 30 and 80 μm.
 8. The anilox roll according toclaim 1, wherein the channel has either a sine-like wave form or asawtooth shape form.
 9. The anilox roll according to claim 1, whereinthe meandering channel has a wavelength that is smaller than 2 times thechannel width.
 10. The anilox roll according to claim 1, wherein saidanilox roll has a total surface and the channel wall has a channel wallsurface taking up less than 10% of said total surface.
 11. The aniloxroll according to claim 10, wherein channel wall surface takes up lessthan 5% of said total surface.
 12. The anilox roll according to claim10, wherein channel wall surface takes up less than 2% of said totalsurface.
 13. The anilox roll according to claim 1, wherein said channelwalls have an amplitude a such that said channel width w2 is equal to asum of two times said amplitude a and an interval t, said interval tbeing less than 10% of said channel width w2.
 14. The anilox rollaccording to claim 13, wherein said interval t is less than 5% of saidchannel width.
 15. A printing apparatus comprising a printing devicehaving a supply for a substrate to be printed and a supply for ink,wherein the printing device comprises an anilox roll according to claim1 mounted in a bearing, as well as a printing roll comprising an imageto be applied to the substrate, wherein the printing roll and the aniloxroll are arranged adjacent to one another, and an axis of rotation ofthe printing roll and an axis of rotation of the anilox roll aresubstantially parallel such that, in operation, the anilox roll isarranged to transfer ink to said printing roll.